VM in Xen 4.1; poor packet forwarding performance on xn0

[Tiago Ribeiro]

> Em 18/04/2014, às 11:57, "seanrees at gmail.com" <seanrees at gmail.com> escreveu:
> 
> Hi there freebsd-xen,
> 
> I tried first on freebsd-questions@ without success, so I thought to retry
> here.
> 
> I run OpenVPN on a FreeBSD 10.0-Rp1 VM in Xen 4.1 (HVM). I am experiencing
> slow network performance on xn0 that seems to have developed after I
> upgraded to FreeBSD 10 (no other changes). I can only achieve about 0.5mbps
> through this interface when forwarding packets; packets in a single
> direction are fine (e.g; downloading to the VPS or pushing from the VPS)
> and clock in at many (>10 usually) mbps.
> 
> Interestingly, my identical VM (configuration managed centrally) running on
> Xen 3.4 (HVM) does *not* have this issue.
> 
> I did a little debugging and here's what I've noticed:
>   - Not related to OpenVPN, repro'd using ssh -d.
>   - Slow VM has a very low rate of context switches (~250) while
> forwarding, fast VM has a lot more (~2000) sampled over 5 seconds using
> systat -v.
>  - I can't repro a context switch limit (tried a limited fork() bomb).
>  - Tried with *and* without LRO and TSO on xn0 (and all combinations of
> LRO and TSO on/off)
> 
> I started digging into the Xen drivers but I realised I am not equipped to
> debug this. I'm looking for suggestions on what to check. My provider is
> offering to move me to an older Xen host but I'd like to see if I can help
> identify a bug either in my configuration or perhaps in FreeBSD's Xen code.
> 
> Sean
> _____________________________________________


Do you use pf?